trait-object-lifetime-parens: improve recovery.

Author: Centril

src/librustc_parse/parser/ty.rs

@@ -148,18 +148,14 @@ impl<'a> Parser<'a> {
             self.parse_impl_ty(&mut impl_dyn_multi)?
         } else if self.is_explicit_dyn_type() {
             self.parse_dyn_ty(&mut impl_dyn_multi)?
-        } else if self.check(&token::Question)
-            || self.check_lifetime() && self.look_ahead(1, |t| t.is_like_plus())
-        {
-            // Bound list (trait object type)
-            let bounds = self.parse_generic_bounds_common(allow_plus, None)?;
-            TyKind::TraitObject(bounds, TraitObjectSyntax::None)
         } else if self.eat_lt() {
             // Qualified path
             let (qself, path) = self.parse_qpath(PathStyle::Type)?;
             TyKind::Path(Some(qself), path)
         } else if self.check_path() {
             self.parse_path_start_ty(lo, allow_plus)?
+        } else if self.can_begin_bound() {
+            self.parse_bare_trait_object(lo, allow_plus)?
         } else if self.eat(&token::DotDotDot) {
             if allow_c_variadic == AllowCVariadic::Yes {
                 TyKind::CVarArgs
@@ -218,6 +214,15 @@ impl<'a> Parser<'a> {
         }
     }
 
+    fn parse_bare_trait_object(&mut self, lo: Span, allow_plus: AllowPlus) -> PResult<'a, TyKind> {
+        let lt_no_plus = self.check_lifetime() && !self.look_ahead(1, |t| t.is_like_plus());
+        let bounds = self.parse_generic_bounds_common(allow_plus, None)?;
+        if lt_no_plus {
+            self.struct_span_err(lo, "lifetime in trait object type must be followed by `+`").emit()
+        }
+        Ok(TyKind::TraitObject(bounds, TraitObjectSyntax::None))
+    }
+
     fn parse_remaining_bounds_path(
         &mut self,
         generic_params: Vec<GenericParam>,

src/test/ui/parser/macro/trait-object-macro-matcher.rs

@@ -2,9 +2,14 @@
 // `ty` matcher in particular doesn't accept a single lifetime
 
 macro_rules! m {
-    ($t: ty) => ( let _: $t; )
+    ($t: ty) => {
+        let _: $t;
+    };
 }
 
 fn main() {
-    m!('static); //~ ERROR expected type, found `'static`
+    m!('static);
+    //~^ ERROR lifetime in trait object type must be followed by `+`
+    //~| ERROR at least one trait is required for an object type
+    //~| WARN trait objects without an explicit `dyn` are deprecated
 }

src/test/ui/parser/macro/trait-object-macro-matcher.stderr

@@ -1,8 +1,22 @@
-error: expected type, found `'static`
-  --> $DIR/trait-object-macro-matcher.rs:9:8
+error: lifetime in trait object type must be followed by `+`
+  --> $DIR/trait-object-macro-matcher.rs:11:8
    |
 LL |     m!('static);
-   |        ^^^^^^^ expected type
+   |        ^^^^^^^
 
-error: aborting due to previous error
+warning: trait objects without an explicit `dyn` are deprecated
+  --> $DIR/trait-object-macro-matcher.rs:11:8
+   |
+LL |     m!('static);
+   |        ^^^^^^^ help: use `dyn`: `dyn 'static`
+   |
+   = note: `#[warn(bare_trait_objects)]` on by default
+
+error[E0224]: at least one trait is required for an object type
+  --> $DIR/trait-object-macro-matcher.rs:11:8
+   |
+LL |     m!('static);
+   |        ^^^^^^^
+
+error: aborting due to 2 previous errors
 

src/test/ui/parser/trait-object-lifetime-parens.rs

@@ -6,10 +6,7 @@ fn f<'a, T: Trait + ('a)>() {} //~ ERROR parenthesized lifetime bounds are not s
 
 fn check<'a>() {
     let _: Box<Trait + ('a)>; //~ ERROR parenthesized lifetime bounds are not supported
-    let _: Box<('a) + Trait>;
-    //~^ ERROR expected type, found `'a`
-    //~| ERROR expected `while`, `for`, `loop` or `{` after a label
-    //~| ERROR expected expression, found `)`
+    let _: Box<('a) + Trait>; //~ ERROR lifetime in trait object type must be followed by `+`
 }
 
 fn main() {}

src/test/ui/parser/trait-object-lifetime-parens.stderr

@@ -10,25 +10,11 @@ error: parenthesized lifetime bounds are not supported
 LL |     let _: Box<Trait + ('a)>;
    |                        ^^^^ help: remove the parentheses
 
-error: expected `while`, `for`, `loop` or `{` after a label
-  --> $DIR/trait-object-lifetime-parens.rs:9:19
-   |
-LL |     let _: Box<('a) + Trait>;
-   |                   ^ expected `while`, `for`, `loop` or `{` after a label
-
-error: expected expression, found `)`
-  --> $DIR/trait-object-lifetime-parens.rs:9:19
-   |
-LL |     let _: Box<('a) + Trait>;
-   |                   ^ expected expression
-
-error: expected type, found `'a`
+error: lifetime in trait object type must be followed by `+`
   --> $DIR/trait-object-lifetime-parens.rs:9:17
    |
 LL |     let _: Box<('a) + Trait>;
-   |         -       ^^ expected type
-   |         |
-   |         while parsing the type for `_`
+   |                 ^^
 
-error: aborting due to 5 previous errors
+error: aborting due to 3 previous errors